The present disclosure relates to a power amplification module.
A power amplification module is used in a mobile communication device such as a cellular phone in order to amplify the power of a radio frequency (RF) signal to be transmitted to a base station. A bias circuit is used in a power amplification module. The bias circuit is for supplying a bias current to a power amplification transistor. For example, Japanese Unexamined Patent Application Publication No. 10-135750 discloses a power amplification module that includes a plurality of amplification stages in which transistors are used as amplification elements. The power amplification module disclosed in Japanese Unexamined Patent Application Publication No. 10-135750 is configured such that an initial stage bipolar transistor and a final stage bipolar transistor each have a common emitter, and the initial stage bipolar transistor is made to operate in a base current constant mode and the final stage bipolar transistor is made to operate in a base voltage constant mode.
However, in the power amplification module disclosed in Japanese Unexamined Patent Application Publication No. 10-135750, the gain falls as the output power increases and consequently the linearity of the power amplification module is degraded.